it won't collect algae unless you are feeding heavily, or not keeping up with waterchanges...just like in your main tank. i have alot of lps in my frag/prop tank and feed them heavily, so i had a ton of algae all over the egg crate, but i've seen other people who target feed much less with perfectly clean(besides some coralline algae) egg crate. egg crate is going to act like any other surface.